If it is a closed loop cruise, like starting and returning to an American cruise port, then you can use a valid ID or Birth Certificate. However, if you are getting off the ship in an international port then a Passport is required. I would suggest you get a passport. Cruises leaving from an American cruise port have to stop at an International cruise port and if something was to happen and you needed to get off the ship and return to the USA, then a passport would make that easier.
Wait why did you need your passport? I thought you didn’t need it when going out of the country on a cruise
Yes, you will need a passport or a birth Certificate in order to get aboard a cruise ship.
If it is a closed loop cruise, like starting and returning to an American cruise port, then you can use a valid ID or Birth Certificate. However, if you are getting off the ship in an international port then a Passport is required. I would suggest you get a passport. Cruises leaving from an American cruise port have to stop at an International cruise port and if something was to happen and you needed to get off the ship and return to the USA, then a passport would make that easier.